The present invention was developed in connection with motor control circuitry for motor driven door operators, for example of the kind usable for opening and closing garage doors. A persistent problem in this field, which insofar as I am aware has gone without satisfactory solution, is that of preventing automatic restarting of the door operator motor after a temporary interruption of energizing current flow through such motor. A typical electric door operator motor is reversible and incorporates a pair of windings connected at one end through a thermal overload protector to an external motor terminal and at their other, free ends to respective further motor terminals. A temporary break may occur in the path between motor windings and the electrical supply due to opening of the thermal overload protector in the motor. However, this is not the only possible cause for a temporary break in current supply to the motor windings. For example, a temporary power outage can occur at some location remote from the door, as due to storm damage to commercial power lines serving the door operating circuit. An automatic restarting of the motor, e.g., upon cooling of the thermal overload protector, restoration of the commercial power line, etc., may occur when least expected by the person using the door. Thus, unexpected restarting of door movement could damage persons or property in the path of the door. Thus, a restart prevention control incapable of preventing automatic restart after various types of temporary power interruption, or requiring extra or non-standard motor termination, is not satisfactory.
Accordingly, it is an object of this invention to provide:
A motor control circuit for preventing automatic restarting of an electric motor following an interruption of electric current flow therethrough.
A control circuit as aforesaid usable in a door operator circuit, as for garage doors.
A circuit as aforesaid usable with electric motors internally connecting an automatic reset thermal overload protector to the free ends of a pair of motor windings, in common, without availability of an external connection between said windings and protector.
A circuit as aforesaid capable of preventing automatic restarting of the motor not only in the event of a temporary motor shut-off by the motor thermal overload protector, but also due to other temporary interruptions of current to the motor including those due to conditions outside the motor, e.g., in power lines from a commercial power company.
A circuit as aforesaid which, after restoration of the thermal overload protector to its normal operating condition, or elimination of other causes of temporary current failure to the motor, will permit intentional reenergization of the motor in a convenient manner, as by actuation of the normal door operating switch, or start switch, without need for direct manual contact with the motor itself.
A circuit as aforesaid which can readily control additional and/or accessory devices, in concert with actual current flow through the motor, e.g., to operate a brake when and only when the motor is running.
A circuit as aforesaid wherein extra cost and structural complexity, occasioned by provision of automatic restart prevention, are minimized.
Other objects and purposes of this invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.